This invention relates mechanical drives and more particularly to a clutch-brake unit for drives and to a method and jig for installing such clutch-brake units.
The typical press for small bending, blanking, and similar operations has a crankshaft which rotates in a frame to reciprocate a ram which actually performs the bending, blanking, or other deforming operation. The crankshaft at one end carries a large flywheel which is powered by an electric motor and normally rotates freely on the crankshaft. Some type of clutch is normally between the flywheel and the crankshaft to couple the two together when engaged, and this imparts rotation to the crankshaft. After one revolution the clutch disengages and a brake is applied to stop the crankshaft. During the single revolution, the ram moves downwardly and retracts to its initial position.
Most presses in operation today have a so-called mechanical clutch, which is merely a mechanism that projects a dog from the flywheel into the crankshaft to couple the two together. These clutches are subjected to substantial impacts each time they are engaged and as a result, fail quite frequently. This causes down time which might otherwise be put to productive use. Furthermore, these clutches provide a positive connection between the flywheel and crankshaft, and as a result, dies and various components of the press are often damaged when a jam occurs. Normally, the mechanical clutch is at one end of the crankshaft and a brake is at the other end, and sometimes difficulty is encountered coordinating the two so that the crankshaft will stop precisely at the end of one revolution.
While many existing presses utilize mechanical clutches, most presses of more recent manufacture have been provided with air-operated clutch-brake units. These units employ friction surfaces for both driving and braking. When the clutch is supplied with pressurized air, the clutch is engaged, causing the crankshaft to turn with the flywheel. On the other hand, when the air pressure is released, the clutch disengages and the brake is applied. Since friction surfaces are employed, slippage may occur, and this reduces the severity of shocks and furthermore diminishes the chance of damage due to jams. Moreover, the clutch and brake are precisely coordinated so that when one is applied, the other is released and vice versa.
Since air-operated clutch-brake units are far superior to the mechanical variety, conversion packages have been developed for converting presses having the old mechanical clutches to the air operated clutch-brakes. The conversion packages heretofore developed have been quite difficult to install on existing presses. Most of the difficulty resides in mounting the brake anchor on the frame. Also, installing a hub capable of conveying pressurized air to the clutch has been a major problem.